1. Field of the Invention
The present invention relates to a capacitor and a light emission display panel using the same, and more particularly, it relates to a capacitor formed on a substrate and a light emission display panel including the capacitor.
2. Discussion of the Background
Generally, a flat panel display (FPD) displays images with materials arranged in a closed container formed by providing barriers between sidewalls of two substrates. Various types of FPDs include a liquid crystal display (LCD), which uses liquid crystal cells that change reflectivity in an applied electric field, a field emission display (FED), which uses phosphors excited by an electron stream, and an organic electro-luminescent display, which uses electroluminescence of organic materials.
FPDs may be driven by passive matrix and active matrix driving methods. The active matrix method uses a thin film transistor (TFT). In the passive matrix method, an anode and a cathode cross each other, and a line is selected to drive the organic light emitting cells. However, in the active matrix method, which uses a thin film transistor (TFT), each pixel electrode is coupled to the TFT, and the light emitting cell is driven in accordance with a voltage maintained by a capacitor coupled to the TFT's gate electrode.
FIG. 1 is an equivalent circuit diagram showing an organic electro-luminescent display device employing a conventional active matrix method.
Referring to FIG. 1, a pixel circuit of the organic electro-luminescent display device may include an organic electro-luminescent device (OLED), a switching transistor SM, a driving transistor DM, and a capacitor C. A source of the driving transistor DM is coupled to a power voltage VDD, and a capacitor C is coupled between the driving transistor's gate and source. The capacitor C maintains a gate-source voltage VGS of the driving transistor DM for a predetermined period of time. The switching transistor SM transmits a data line Dm data voltage to the driving transistor DM in response to a selection signal transmitted from a current scan line Sn. A cathode of the OLED is coupled to a reference voltage Vss, and the OLED emits light corresponding to a current applied thereto through the driving transistor DM.
In the active matrix method, each pixel circuit may include a TFT and a capacitor, and the TFT is driven by the voltage maintained by the capacitor for a predetermined period of time. Accordingly, each pixel circuit may continuously display images corresponding to data signals for one frame. Thus, the active matrix method is commonly used because it is superior to the passive matrix method.
FIG. 2 is a sectional view showing a configuration of a capacitor formed in a conventional display panel.
Referring to FIG. 2, a buffer layer BL is formed on a substrate ST, and a first conductive layer CL1, which forms the capacitor's first electrode, is formed on the buffer layer BL. A dielectric layer DL is formed on the conductive layer CL1, and a second conductive layer CL2, which forms the capacitor's second electrode, is formed on the dielectric layer DL. Thus, the capacitor includes the first and second conductive layers CL1 and CL2. Such a capacitor is typically formed in an area where a pixel circuit is formed, and the capacitance of the capacitor varies depending on the display panel's characteristics.
However, if using the active matrix method, the display panel's pixel area also includes a TFT. Therefore, an area in which display elements are formed may be reduced. In other words, the display panel's aperture ratio may be reduced, thereby degrading the display's quality.
In particular, an organic electro-luminescent display may use a pixel circuit having more than two capacitors and a plurality of TFTs to compensate for the driving transistor's threshold voltage, which may result in a low aperture ratio. Therefore, a capacitor occupying less space in the pixel area while providing a required capacitance is desired.